Pulse torque control apparatus



Nov. 21, 1967 A D ET AL 3,354,366

PULSE TORQUE CONTROL APPARATUS Original Filed April 6, 1962' 2Sheets-Sheet 1 FIG. I

CONSTANT CURRENT SOURCE u BI/ '62 F? 0 OFF PULSE on PuLsE COMPUTERCONSTANT PULSE SOURCE COMPUTER INVENTOR. ARNEY LANDY, JR. TENNY D. LODEATTORNEY.

Nov. 21, 1967 ANE, R ET AL 3,354,366

PULSE TORQUE CONTROL APPARATUS Original Filed April 6, 1962 2Sheets-Sheet 2 CURRENT o FLONING IN T G (nonh) :"rwm H H l! I PULSES OFF\ A k l Al I l l A I 22:15:) n3 I/IIZZ (28' I V i I I v I v I ll|7 r l lI l l APPLIED TO FFB4 AND FF :01 L A l I l I CURRENT FLowmG m TG (anINVENTOR. F] G 2 ARNEY LANDY, JR.

ATTOR NEY.

United States Patent ()fiice ABSTRACT OF THE DISCLOSURE This applicationdiscloses a pulse torquer for inertial instruments wherein a digitallycontrolled switching bridge causes energization pulses to be applied tothe torquer in a plus or minus direction. When the torquer is at or nearnull, alternate plus and minus pulses are applied.

Cross-reference to related application This application is acontinuation application, Ser. No. 185,623, filed abandoned.

of our copending Apr. 6, 1962, noW

The invention ,This invention relates to apparatus for energizing aforce producing means and more specifically to apparatus forcontinuously pulsing force producing means.

Prior art devices which utilize pulses of power to energize forceproducing means such as torque generators or rebalancing means ofdevices such as sensitive gyros and accelerometers land the like usuallyapply the pulses to the force producing means only when it is desired toobtain a force. This type of device is commonly known as a pulse ondemand device. To illustrate the operation of this device assume that itis desired to maintain a gyro, having a torque generator and a signalgenerator, in some relative position. If the gyro leaves this relativeposition the signal generator produces a signal which is applied to apulse generator and the pulse generator produces pulses of the properpolarity which when applied to the torque generator winding cause thegyro to assume its relative position.

In some of the more sophisticated prior art devices when the gyro was ata null position, or in the position at which it was desired to maintainit, the pulses from the pulse supply were applied to a dummy load. Thedummy load is an impedance which is as similar to the impedance of thetorque generator winding as is practical. When the pulse supply isswitched from the dummy load to the torque generator winding, slightchanges in the pulses occur dueto the change in load across the pulsesupply. Since the dummy load cannot be made exactly the same impedanceas the torque generator winding the load of the pulse supply will alwayschange when switching from one to the other. Because the accuracy ofthis device is dependent upon the exactness with which all of the pulsesmay be produced equal, these changes in pulses due to changes in theload may cause a large variation in accuracy. Also, the switching meansis of necessity quite complicated'to accomplish the switching from thedummy load to the torque generator in the correct polarity and for thecorrect length of time.

In the present invention an energization source, which may be a constantcurrent source or a constant pulse source, is connected to some forceproducing means such as the torque generator of a gyro by a switchingmeans. The switching means may be comprised of some type of solid stateswitches or some type of mechanical switches depending upon the use ofthe device and the speed with which the switching must be done. If theconstant current source is used the switching means alternately 3,3543%Patented Nov. 21, 1967 connects the current source across the torquegenerator Winding, first in one polarity and then in the other while thegyro is at the null position. The switching means operates atpredetermined increments of time, and current is flowing in onedirection or the other through the torque generator winding at all timesthat the switch is not opertaing but flows through a closely matcheddummy load at times that the switch is operating. Thus, pulses ofcurrent are flowing through the torque generator winding at all times,regardless of the position of the gyro. If the gyro moves oif the nullposition the switching means connects the current source to the torquegenerator winding in the same polarity in each switching cycle until thegyro moves back to the null position, at which time the switching meansagain begins to connect the current source alternately plus and minus.Since the constant current source is connected to the dummy load for aconstant amount of time during each cycle the dummy load has the sameeffect on each pulse and its effect becomes a constant which may bepractically removed. Thus, the adverse influence which the dummy loadhas upon the torquing accuracy is greatly reduced.

If a constant pulse supply is utilized in place of a constant currentsource the dummy load may be eliminated completely from the circuit. Toinsure that large values of currents are not being switched, with theresulting bad effects that this produces, the switching is accomplishedbetween pulses. That is, when the gyro is at the null position theswitching means is alternately applying pulses of opposite polarity andthe switching means operates as each pulse comes back to zero. If thegyro moves off of the null position in one direction or the other theswitching means applies a series of positive or negative pulses to thetorque generator winding until the gyro is torqued back to the nullposition at which time the switching means again applies alternatelypositive and negative pulses.

Thus, it can be seen that the present device has substantiallyeliminated the adverse effects which the dummy load has upon theaccuracy of the torque generator and it has greatly simplified theswitching means. Also, by applying continuous plus and minus pulses tothe torque generator winding when the gyro is at the null position adithering effect is obtained which greatly reduces errors due to nulluncertaintities and residual magnetism as well as reducing thresholds.

7 It is a primary object of this invention to provide an improvedcontrol apparatus.

It is a further object of this invention to provide a new and improvedmeans for energizing force producing means.

It is a further object of this invention to provide a simpler and moreaccurate apparatus for energizing such devices as torque generators ofgyros.

These and other objects of this invention will become apparent from thefollowing description of a preferred form thereof in the accompanyingspecification, claims, and drawing, of which:

FIGURE 1 isa block diagram of the present apparatus; FIGURE 2 is adiagram of the pulses present within the apparatus; and

FIGURE 3 is an alternate embodiment of the present apparatus.

In FIGURE 1 the output of a constant current source 10 is connected to ajunction point 11 by means of a lead 12. A switch 13 is connected tojunction point 11 by means of a lead 14 and a switch 15 is connected tojunction point 11 by means of a lead 16. Switch 13, when closed,connects one side of an impedance 20 to junction point 11 and the otherside of impedance 20 is connected to ground. The activation of switch 13is controlled bya signal which is supplied to the switch by means of alead 21 connected at the other end to a bistable flip-flop circuit 22.The activation of switch 15 is controlled by a signal applied to theswitch by means of a lead- 23, which is connected at the other end tothe opposite level of flipilop 22 to that of lead 21. That is, when thesignal on lead 21 and, therefore, switch 13 is an ON signal the signalon lead 23 and, therefore, switch 15 is an OFF signal. Switch 15 whenactivated connects lead 16 to a lead 25 which has the opposite endconnected to a junction point '26. Junction point 26 is connecteddirectly to a first switch '27 and to a second switch 28 by means of alead 29'. Switch 27, when activated, connects junction point 26 to ajunction point 30 by means of a lead 31. Switch 28, when activated,connects'lead 29 to a lead 36 which is connected to a second junctionpoint 35. Connected be tween junction point 30 and junction point 35 isa torque generator winding 32 for a sensitive device such as a gyro oraccelerometer, which is shown schematically as a north gyro 33. Itshould be noted that the winding 32 could represent any force producingmeans and the torque generator has simply been chosen for simplicity inexplanation. Also, to show one possible utilization of the presentinvention the torque generator will be assumed to be the torquegenerator of the north gyro on a stable platform. Another switch 37 isconnected to junction point 30 by means of a lead 38. When activated,switch 37 connects output .on lead N which is applied to switches 28 and37. When a signal is applied to .lead N, switches 28 and 37 areactivated, or closed, which connects the torque generator winding 32 tothe current source 10 in a first orienta tion and, assuming (for themoment) that lead 43 is grounded, current will flow from constantcurrent source 10 through switch 23, torque generator 32 as shown by thearrow marked with a sign, switch 37, and to ground each time switch isactivated by a pulse from flipfiop 22.

If the north gyro should move from the null position in a negativedirection or sense, computer 60 would apply a pulse to flip-flop 50 onlead 64. This pulse would cause lead 38 to a junction point 39. Anotherswitch 40 is con- 7 nected to junction point 35 by means of a lead 41.When activated, switch 40 connects lead 41 to a junction point 42.Junction points 39 and 42 are connected together by means of a lead 43.

Switch 27 is activated by means of a signal which is applied on a leaddesignated P,,. In this particular embodiment of the invention *P standsfor positive north and simply means that when a positive torquing of thenorth gyro is desired this switch is closed. The lead P connected toswitch 27 is actually a continuation of a lead P shown attached to abistable flip-flop 50. Several of the leads have only the endconnectioris shown to reduce confusion in FIGURE 1. However, it shouldbe remembered that the leads having similar letters are in actualityconnected together. Thus, the activation of switch 27 is actuallycontrolled by bistable flip-flop 50. Switch 40 is also activated by asignal which is applied by means of a lead designated P This signal isobtained from the same point on flip-flop 50 as the signal whichactivates switch 27. Switch 28 is activated by a signal which is appliedby means of a lead N Switch 37 is also activated by a signal which isapplied by means of a lead N The leads N connected to switches 28 and 37are extensions of the lead N shownconnected to flip-flop 50. Sinceflip-flop 50 is a bistable device it has two positions a which it maystop. In the first position a signal is applied to lead N which acivatesswitches 28 and'37. When flip-flopSt) is in the second position a signalis applied to the lead P and this signal activates switches 27 and 40. jj

U A suitable computer 60 provides one input for bistable flip-flop 22 ona lead 61 and the other input on alead 62. :Computer '60 also p'rovidesa first input for bis table flip- 'flop 50 on a lead 63 and a secondinput for flip-flop '50 on a lead 64. Computer 60 may be some simpletype of digital computer which applies a steady train of pulses thatalternate between leads 61 and 62 to cause flip-flop 22 to operate at aspecific frequency. Computer will also apply a steady train of pulses toflip-flop 50 which alter: nate betweenleads 63 and 64 when the northgyro is at the null position. As explained more fully later, thesepulses onflip-flop 50 will cause the current from source 10 to flowthrough the north gyro torque generator winding 32 in alternatedirections which causes the gyro to dither or oscillate slightly aboutthe null position. If the north gyro .moved from the null position in apositive direction or sense computer 60 would apply a pulse to flip-fiop50 on lead 63 causing flip-flop 50 to produce an which are applied toflip-flop 22 on flip-flop 50 to produce a signal on lead P which wouldbe applied to switches 27 and 40. The signal on lead l would activate orclose switches 27 and 40, which would connect the torque generatorwinding 32 to the current source 10 in a second orientation, and allowcurrent to flow from the constant current source 10 through switch 27,torque generator 32 in the opposite direction, as shown by the arrowmarked with a sign, and switch 40 to ground. It should be noted thatagain this current will only flow at the times when switch 15 isactivated by pulses from flip-flop 22. When a signal is applied to leadP to activate switches 27 and 40 the lead N has a signal to deactivateswitches 28 and 37, or in some apparatus no signal at all may causethese switches to open.

In a similar manner, flip-flop 22 causes switch 13 to open when switch15 is closed and switch 15 to open when switch 13 is closed. The pulsesfrom computer 60 should be so timed that when flip-flop 50 is activatingswitches to change the direction of the current flow through torquegenerator 32 from a positive to a negative direction or from a negativeto a positive direction switch 15 is opened and switch 13 is closed,thus, allowing the current from the constant source to flow throughimpedance 20. This can easily be accomplished by applying the OFFpulses, lead 61, to either lead '63 or lead 64 depending upon thedirection which it is desired to torque the gyro. These pulses could beapplied to either lead 63 or lead 64 by means of it switch which couldbecontrolled by the, signal generator at the north gyro. Thus, when thesignal generator of the north gyro indicatedthat the gyro had movedin anegative direction the OFF pulses could be applied to lead 64 and,conversely, when the signal generator of the north gyro indicated thatthe gyro had moved in a positive direction the switch could becontrolled to apply the OFF pulses to lead 63. A configuration similarto the above would be utilized in strapped-down systems or where thegyio is to measure the angular rate of a device and is solidly attachedto that device. It should be 'noted that this pulse torquing devicemight also be used in such systems as inertial platforms, in which case,the gyro signal generator is attached to a synchro on one of the gimbalsof the platform and the input to the computer 60 would come "non outputsof accelerometers on the platform. The computer controlled pulse trainwould then be used to phases the platform by the g'yro loop. No detailhas been shownin computer 60 since the components required would tiependstrictly upon the utilization of'the present invention and as manydifferent configurationscould be thought of by one skilled in the art asditfer'ent uses of the present i To connect an east gyro to the presentdevice a switch 70 is connected directly to junction point 39 and aswitch 71 is connected directly to a junction point 42. Switch 70 whenactivated connects junction point 39 toa junction point 73 by means of alead 72. Switch 71 when activated connects junction .point 42 to ajunction point 75 by means of a lead 74. The torque generator winding 76of an east gyro is connected between junction points 73 and 75. An eastgyro is shown schematically at 69. A. switch 77 is connected directly tojunction point 73 and 7 when activated connects junction point 73 to ajunction point 79 by means of a lead 78. A switch 80 is connecteddirectly to junction point 75 and when activated connects junction point75 to a junction point 82 by means of a lead 81. Junction point 79 andjunction point 82 are connected together by means of a lead 83.

Switch 70 is activated by means of a signal applied on a lead P Theother end of lead P is connected to a bistable flip-flop 84. Aspreviously explained for leads N and P only the ends of lead P areshown. Switch 80 is also activated by a signal which is applied on leadP Switch 71 is activated by a signal which is applied on a lead N theother end of the lead N is attached to bistable flip-flop 84. Switch 77is also activated by a signal on lead N As previously explained inrelation to the north gyro, the letters P stand for positive east andthe letters N stand for negative east. These letters are utilized tofurther clarify the operation of the present device. Computer 60controls bistable flip-flop 84 to a negative position by means of asignal on a lead 85 or to a positive position by means of a signal on alead 86.

A third or azimuth gyro torque generator may be connected in series withthe north and east torque generators in the following manner. A switch90 is connected directly to junction point 79 and when activatedconnects junction point 79 to a junction point 91 by means of a lead92.'A switch 93 is connected directly to junction point 82 and whenactivated connects junction point 82 to a junction point 94 by means ofa lead 95. A torque generator winding 96 of an azimuth gyro is connectedbetween junction points 91 and 94. An azimuth gyro is shownschematically at 89. A switch 97 is connected directly to junction point91 and when activated grounds junction point 91 through a lead 98. Aswitch 99 is connected directly to junction point 94 and when activatedgrounds junction point 94 through a lead 100.

Switch 90 is activated by means of a signal applied to a lead P Theother end of lead P is connected to a bistable flip-flop 101. Switch 99is also activated by means of a signal on lead P Switches 93 and 97 areactivated by means of a signal on a lead N the other end of which isconnected to flip-flop 101. As already explained, to simplify FIGURE 1only the end connections of leads P and N are shown. Flip-lop 101 iscontrolled to a negative position by means of a signal applied to aninput 102 thereof by computer 60. Flip-flop 101 is controlled to apositive position by means of a signal applied to another input lead 103thereof by computer 60. Flip-flop 101 acts similar to flip-flops 84 and50. That is, when a pulse is applied to the positive input lead 103 bycomputer 60 the flip-flop is controlled to a position whereby it appliesan activating signal to the positive output lead and a deactivatingsignal to the negative output lead. When a signal is applied to thenegative input lead 102 by computer 60 an activating signal is appliedto the negative output lead and a deactivating signal is applied to thepositive output lead.

The north gyro 33, the east gyro 69, and the azimuth gyro 89 providesignals on leads 104, 105, and 106, respectively, which are coupled tocomputer 60. Computer 60 operates in accordance with these signals inapplying switching signals to flip-flops 50, 84, and 101.

OPERATION To demonstrate the operation of the present device it willfirst be assumed that the north, east and azimuth gyros are all at theirnull positions. In FIGURE 2 a series of pulses labeled ON pulses isshown and this series of pulses is applied to lead 62 of flip-flop 22 bycomputer 60. Similarly, a series of pulses labeled OFF pulses alsodepicted in FIGURE 2 will be applied to lead 61 of flipflop 22 bycomputer 60. Also, in FIGURE 2, the series of square pulses labeledcurrent flowing in T (north) ,are the pulses of current flowing throughthe north torque generator winding 32 as measured from junction point 30to junction point 35 and the series of square pulses labeled currentflowing in T (east and azimuth) are the pulses of current flowingthrough the east and azimuth torque generator windings 76 and 96 asmeasured from points 73 to 75 and 91 to 94, respectively. It should benoted that the east and azimuth gyros are shown singly to demonstratetheir connection in the circuit and that in this explanation they willbe assumed to remain at null. Thus, the same current waveform may beused to illustrate the current through both torque windings.

Assume that flip-flop 50 is in the negative position, that is, anactivating signal is on the lead N and switches 28 and 37 are closedwhile a deactivating signal is on the lead P and the switches 27 and 40are open. When computer 60 applies ON pulses to lead 62 flip-flop 22applies an activating signal to switch 15 and a deactivating signal toswitch 13. Assuming that switches 71, 77, 93 and 97 are activated in asimilar manner to switches 28 and 37, when switch 15 closes a pulse ofcurrent will flow through the north torque generator winding 32 fromswitch 28 to switch 37, through the east torque generator winding 76from switch 71 to switch 77 and through the azimuth torque generatorwinding 96 from switch 93 to switch 97. Some specified time latercomputer 60 applies an OFF pulse 111 to lead 61 which switches flip-flop22 deactivating switch 15 and activating switch 13. The deactivation ofswitch 15 stops the current from flowing through the torque generatorcircuit and the activation of switch 13 causes the current to flow downthrough the dummy load 20. The waveform of the current which is flowingthrough north torque generator winding 32 is represented by the squarepulse 112 in FIGURE 2 and the current flowing through the east andazimuth torque generator windings 76 and 96, respectively, isrepresented by the square pulse 142.

If the OFF pulse 111 from the computer 60 is applied to lead 64, lead 86and lead 103 at the same time that it is applied to lead 61, asindicated by pulses 113 and 114, all of the positive or P leads willhave activating signals on them while all of the negative or N leadswill have deactivating signals on them. Thus, when the next ON pulse 115is applied to lead 62 and flip-flop 22 activates switch 15 anddeactivates switch 13, current will flow from the constant currentsource through the north torque generator winding 32 from switch 27 toswitch 40, through the east torque generator winding 76 from switch 70to switch 80 and through the azimuth torque generator winding 96 fromswitch 90 to 99. This current through the torque generator windings iscontinuous until some time later when an OFF pulse 116 is applied tolead 61 causing flip-flop 22 to apply a deactivation signal to switch 15and an activating signal to switch 13. Thus, the current flowing throughthe north torque generator winding 32 is represented by the positivesquare pulse 117 and the current flowing through the east and azimuthtorque generator windings 76 and 96, respectively is represented by thesquare pulse 143.

At the same time that OFF pulse 116 is applied to lead 61 by computer 60the same pulse would be applied to lead 63, lead 85, and lead 102, asrepresented by pulses 117 and 118 in FIGURE 2. These pulses applied toflipflops 50, 84 and 101 would cause the flip-flops to apply anactivation signal to the N leads and a deactivation to the P leads.Thus, when the next ON pulse 119 was applied to lead 62 to activateswitch 15 the current from the constant current source 10 would flowthrough the torque generator windings in a negative direction until thenext OFF pulse 120 was applied to lead 61 and flipflop 22 deactivatedswitch 15. The current flowing through the north torque generatorwinding 32 would produce a negative square pulse as represented by pulse121 and the current flowing through the east and azimuth torquegenerator windings 76 and 96 is represented by pulse 144.

As can be seen in FIGURE 2, when the gyros are at the null position,alternate positive and negative pulses of current are applied to thetorque generator windings which cause the gyros to dither or oscillateslightly about the null position. However, it should be noted that thetime average of the torquing is zero and, hence, the gyro essentiallyremains at the null position. The dithering of the gyro greatly reducesnull uncertainties and thresholds and is also greatly advantageous inthat the switching is greatly simplified by allowing the pulses ofcurrent to flow through the torque generator windings continuously. Theswitch 13 and the dummy load 20 shunt the current from source during theswitching operations to reduce the adverse effects that occur when thecurrent through the torque generator winding is quickly reversed. Byconnecting the dummy load 20 to the source 10 for a specified amount oftime each cycle the eiiect which the dummy load 20 has on the source 10is a constant and. compensation can be introduced in the apparatus or insome cases the constant current source can monitor and, thus, regulateonly the current flowing through the torque windings of the gyros and inthese cases the dummy load would not have any effect on the regulationof the constant current source. Also, it is well known in the art thatpulses of current produce a more linear torquing of the gyro than analogcurrents because the current amplitude is always the same in pulsetorquing.

Assume now that the north gyro moves off the null position in thenegative direction, but the east, and azimuth gyros remain at theirrespective null positions. The OFF pulse 120 which is applied to lead 61by computer 60 is also applied to lead 64, lead 86, and lead 103 asrepresented by pulses 122 and 123. Thus, the flipflops produce anactivating signal on all of the P leads and a deactivating signal on allof the N leads. When the next ON pulse 124 is applied to lead 62flip-flop 22 activates switch and deactivates switch 13 and current isallowed to flow through the torque generator windings 32, '76 and 96 ina positive direction. When the next OFF pulse 125 is applied to lead 61flip-flop 22 deactivates switch 15 and activates switch 13 stopping thecurrent from constant current source 10 from flowing through the torquegenerator windings and shunting it through the dummy load 20. Thepositive square pulse of current through the north torque generatorwinding 32 is repre sented by square pulse 126 and the positive squarepulse of current through the east and azimuth torque windings 76 and 96is represented by the square pulse 145.

At the same time that O-FF pulse 125 is applied to lead 61 the pulse isalso applied to leads 85 and 102 as represented by pulse 127. However,since the north gyro is still cit" null in a negative direction the OFFpulse is applied to the positive lead 64 of flip-flop 50. This isrepresented by pulse 128. Thus, while the current through the easttorque generator winding 76 and the azimuth torque generator winding 96is switched to flow in a negative direction the current through the.north torque generator winding 32 is still traveling in a positivedirection to torque the gyro back towards null. This second positivepulse of current through the north torque generator is represented bythe positive square pulse 12-9 and the negative pulse though the eastand azimuth torque generator windings 76 and 96 is represented by squarepulse 146.

Assume that after another positive square pulse of current 130 isapplied to the north torque generator winding 32 the north gyro again isat a null position and the current again begins to alternate through thenorth torque generator winding 32 as previously explained and as shownby square pulses 131, 132 and 133. If now the north gyro should movefirom the null position in a positive direction the pulses of currentwould continue to travel through the north torque generator winding 32in a negative direction, as shown by pulses 134 and 135, to torque thegyro backto the null position. Once the gyro reached the null positionthe pulses would again alternate as shown by pulses 136 and 137.Meanwhile the east and azimuth gyros Thaveremained at the null positionand alternate positive and negative pulses 147 through 154 have beenapplied to torque windings 76 and 96. Thus, the east and azimuth gyroshave been continually. dithered about the null position. To producecurrent pulses 13.0 to 137 and 147 to 154. all of the flip-flops andswitches are activated by pulses from the computer 60 as alreadyexplained and as shown in FIGURE 2.

The maximum amount of torque which any of the torque generators canproduce occurs when all of the square pulses of current applied to thetorque generator windings are applied in the same direction, and theamount of torque can be linearly decreased by decreasing the net numberof pulses of current in that particular direction. The net number ofpulses may be defined as the diiference between the number of pulses ofopposite polarity. When the number of pulses traveling through thetorque generator winding in one direction is exactly equal to the numberof pulses traveling through the torque generator winding in the otherdirection the torque generator will produce no net torque. However,since each pulse of current applied tothe torque generator windingcauses the torque generator to produce a small amount of torque whenalternate positive and negative pulses are applied to the torquegenerator winding an alternative positive and negative torque will beproduced which will cause the gyro to oscillate slightly or dither. Thisdither is advantageous in that it will reduce thresholds and nulluncertainties in the gyro and torque generator, as well as reducing theaverage residual magnetism in the torque generator core.

Thus, the present invention is a highly accurate device utilizing acontinuous train of pulses for energizing force producing means in thatthe size and, therefore, the consistency of the pulses applied to theforce producing means is dictated by a separate pulse device which isnot effected by the slight changes in load which occur when the dummyload is exchanged for the torque generator winding. Also, the device issimple to construct and has the added features that it reducesthresholds and null uncertainties as well as average residual magnetismin the core of the force producing means.

Another possible configuration which is within the scope of the presentinvention is to exchange the constant current source 10 with a constantpulse source 210 shown in FIGURE 3. In this embodiment the dummy load 20and its associated circuitry, switch 13, switch 15, and flipflop 22, maybe eliminated. This can be accomplished by simply actuating switch 15 orby taking these components out of the circuit as shown in FIGURE 3.Then, if the flip-flops 50, 84 and 101 are triggered when the output ofthe constant pulse source is zero, the same eifect will be obtained asdescribed in the previous embodiment. As shown in FIGURE 3 constantpulse source 210 applies a series of constant pulses to a junction point226 by means of a lead 212 and to a computer 260 by means of a lead 219.The computer 260 applies a pulse to a flipflop 250 on either a negativelead 263 or a positive lead 264. The constant pulse source 210 isconnected to computer 260 so that the computer will energize flip-flop250 between pulses from source 210. A switch 227 is con nected directlyto junction point 226 and when activated connects junction point 226 toanother junction point 230 by means of a lead 231. Another switch 228 isconnected to junction point 226 by means of a lead 229 and whenactivated connects junction point 226 to another junction point 235 bymeans of a lead 236. A north gyro torque generator winding 232 isconnected between junction points 230 and 235.- Also, connected tojunction point 230 by means of a lead 238 is a switch 237 and connectedto junction point 235 by means of a lead 241 is a switch 240. Switch237, when activated, connects lead 238 to ground by means of a lead 243and switch 240, when activated, connects lead 241 to ground by means oflead 243. Switches 227, 228, 237 and 240 are connected to flip-flop 250by P and N leads in the same manner as already explained for theprevious embodiment. It should be noted that lead 243 is shown groundedand only the north torque generator winding is depicted for simplicity.The operation of this embodiment is similar to the embodiment previouslydescribed except that the dummy load 20 and its associated circuitry hasbeen eliminated because a constant pulse supply 210 is utilized. In thisembodiment the adverse eifect which the dummy load has on the accuracyof the torquing is eliminated and the advantage of the dither producedby the torque generator are still prevalent.

While we have shown and described a preferred embodiment of thisinvention, further modifications and improvements will occur to thoseskilled in the art. We desire it to be understood, therefore, that thisinvention is not limited to the particular form shown and we intend inthe appended claims to cover all modifications which do not depart fromthe spirit and scope of this invention.

We claim:

1. Apparatus for energizing reversible force producing means comprising,in combination: an energization source for providing pulses ofsubstantially constant energy content; switching means; and controlmeans connected to said switching means for operating said switch ingmeans for periodically connecting said energization source to the forceproducing means in a first orientation when a first sense of force isdesired so that said pulses are applied to said force producing means ina first sense, in a second orientation when a second sense of force isdesired so that said pulses are applied to said force producing means ina second sense, and alternately in the first and second orientationswhen substantially no force is desired so that said pulses arealternately applied to said force producing means in the first andsecond senses.

2. Apparatus for substantially rebalancing the movable member of aninertial sensor comprising, in combination: reversible force producingmeans connected in an operable relationship with the inertial sensor;means for supplying energization pulses, each pulse liavingsubstantially constant energy content; switching means for connectingsaid means for supplying energization pulses to said force producingmeans, said connection being in a first orientation when a firstdirection of movement of the movable member is desired so that theenergization pulses are applied to said force producing means in a firstsense only, in a second orientation when a second direction of movementof the movable member is desired so that the energization pulses areapplied to said force producing means in the second sense only, andalternately in the first orientation and then in the second orientationwhen substantially no movement of the movable member is desired so thatthe pulses are alternately applied to said force producing means in thefirst and second senses; and means connected to the switching means forselectively activating said switching means to connect the means forsupplying energization pulses to the force producing means in thedesired orientation.

3. Apparatus as defined in claim 2 in which the means for supplyingenergization pulses includes a constant current source, a dummy loadmeans, second switching means for alternatively connecting said constantcurrent source to said dummy load means or to said first mentionedswitching means, and means connected to said switching means foractivating said switching means.

4. Apparatus as defined in claim 2 in which the switching means includesfirst, second, third, and fourth switches connected to form a switchingbridge, the force producing means being connected across one diagonal ofsaid switching bridge and the means for supplying energization pulsesbeing connected across another diagonal of said switching bridge.

5. Apparatus as defined in claim 4 in which the means for selectivelyenergizing said switching means includes a bistable means having firstand second output means maintained in respectively opposite signalconditions, means connecting said first output means to a first pair ofswitches of the switching bridge whereby said first pair of switches isenergized when said bistable means is in a first state and furtherconnecting said second output means to a second pair of switches of theswitching bridge whereby said second pair of switches is energized whensaid bistable means is in a second state, and means connected to saidbistable means for reversing the state thereof.

6. Apparatus for controlling a movable member having reversible forceproducing means attached thereto capable of moving said member relativeto a null position comprising, in combination: a constant currentsupply; switching means for periodically connecting said current supplyto said force producing means of said member to form pulses ofsubstantially constant energy content; and control means connected tosaid switching means for switching said switching means to a firstcondition so that pulses are applied to said force producing means onlyin a first sense to move said member in one direction toward null, to asecond condition so that pulses are applied to said force producingmeans only in a second sense to move said member in the other directiontoward null, or alternately to said first condition and then to saidsecond condition to maintain said member approximately at the nullposition; a dummy load; and means for connecting said dummy load to saidconstant current supply except when said switching means is connectingsaid constant current supply to said force producing means.

7. Apparatus for digitally rebalancing an inertial sensor comprising, incombination: force generating means positioned in operable relationshipto a movable member of said intertial sensor for producing movement ofsaid movable member when said force generating means is energized; apulse source for producing pulses having a substantially constantquantity of electrical energy in each pulse; first switching means forconnecting said pulse source to said force generating means in a firstsense; second switching means for connecting said pulse source to saidforce generating means in a second sense; means for activating saidfirst and second switching means to connect said pulse source to saidforce generating means only in the first sense when a first direction ofmovement of said movable member is desired, only in a second sense whena second direction of movement of a movable member is desired, andalternately in the first and second sense when substantially no movementof said movable member is desired.

8. Apparatus as defined in claim 7 in which the first switching meansincludes first and second switches and the second switching meansincludes third and fourth swtiches and means connecting said first,second, third and fourth switches to form a switching bridge, the forceproducing means being connected across one diagonal of said switchingbridge and the means for supplying energization pulses being connectedacross another diagonal of said switching bridge.

References Cited UNITED STATES PATENTS 2,533,695 12/ 1950 Sc'hrieber318-129 2,753,505 7/1956 Larew et al 318-28 2,888,622 5/1959 Mooers318-293 2,907,213 10/1959 Wendt 74-5.47 2,990,505 6/ 1961 Ketchledge318-281 3,004,199 10/1961 Sakson 318-28 3,078,404 2/1963 Dumaire 318-1623,079,539 2/ 1963 Guerth 318-28 3,110,851 11/1963 Plogstedt et al.318-29 3,176,143 3/1965 Lode 307-41 BENJAMIN DOBECK, Primary Examiner.

1. APPARATUS FOR ENERGIZING REVERSIBLE FORCE PRODUCING MEANS COMPRISING,IN COMBINATION: AN ENERGIZATION SOURCE FOR PROVIDING PULSES OFSUBSTANTIALLY CONSTANT ENERGY CONTENT; SWITCHING MEANS; AND CONTROLMEANS CONNECTED TO SAID SWITCHING MEANS FOR OPERATING SAID SWITCHINGMEANS FOR PERIODICALLY CONNECTING SAID ENERGIZATION SOURCE TO THE FORCEPRODUCING MEANS IN A FIRST ORIENTATION WHEN A FIRST SENSE OF FORCE ISDESIRED SO THAT SAID PULSES ARE APPLIED TO SAID FORCE PRODUCING MEANS INA FIRST SENSE, IN A SECOND ORIENTATION WHEN A SECOND SENSE OF FORCE ISDESIRED SO THAT SAID PULSES ARE APPLIED TO SAID FORCE PRODUCING MEANS INA SECOND SENSE, AND ALTERNATELY IN THE FIRST AND SECOND ORIENTATIONSWHEN SUBSTANTIALLY